The object of the invention is to develop a new process for the production of 3-methylmercapto-4-amino-6-t-butyl-1,2,4-triazin-5-one, which is a known herbicide, and for the production of 3-methylmercapto-4-amino-6-(1-methyl-cyclopropyl)-1,2,4-triazin-5-one which has not previously been described and likewise is effective as a selective herbicide. The above-mentioned 6-(1-methyl-cyclopropyl) compound can be used in the same way and against the same plants as the known 6-t-butyl compound also mentioned above.
The 3-methylmercapto-4-amino-6-t-butyl-1,2,4-triazin-5-one can be produced for example according to the process described in German OS No. 2,165,554 by reaction of pivaloyl chloride with an isonitrile, the imidchloride formed hydrolyzed to an .alpha.-ketocarboxylic acid amide and the amide further reacted with thiocarbohydrazide in a polar solvent, in a given case in the presence of an acid catalyst. The disadvantage of this process is that it goes circuitously by way of the very ill-smelling and very expensive isonitriles. Besides the 3-mercapto compound can only be obtained in yield of 60% to 79%.
The 1-methyl-cyclopropyl compound set forth above can be used as a herbicide in the manner taught in German OS No. 2,165,554.